Recently, there has been an increasing interest in energy storage technology. Electrochemical devices have been widely used as energy sources in the fields of cellular phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development into them.
In this regard, electrochemical devices are one of the subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention. Recently, research and development of such batteries are focused on the designs of new electrodes and batteries to improve capacity density and specific energy.
Many secondary batteries are currently available. Among these, lithium secondary batteries developed in the early 1990's have drawn particular attention due to their advantages of higher operating voltages and much higher energy densities than conventional aqueous electrolyte-based batteries, for example, Ni-MH, Ni—Cd, and H2SO4—Pb batteries.
Generally, secondary batteries are constructed by embedding an electrode assembly consisting of an anode, a cathode, and a separator interposed therebetween in the form of a laminated or wound structure in a battery case and introducing a non-aqueous electrolyte solution therein.
As the anode, a lithium electrode has often been used, the lithium electrode being generally formed by attaching a lithium foil on a planar current collector. While a battery having such a lithium electrode operates, electrons transfer through the current collector into the lithium foil to make a unidirectional flow. From this, electron density on lithium surface becomes un-uniform, and thus lithium dendrites may be formed. The lithium dendrites may cause damage on the separator and a short circuit in the lithium secondary battery.
In order to solve this problem, there has been an attempt that the top of lithium surface is coated with a protective membrane for lithium ion conduction, thereby preventing the formation of lithium dendrites. However, the protective membrane for lithium ion conduction is often peeled off by the decrease and increase of lithium during the charge and discharge of batteries.